Fixed in hrev39891. It definitely works. If individual partitions fail to mount, it's a different problem. In some circumstances, all your unmounted partitions may fail to mount for another problem, but this function in DriveSetup works as intended.

I tested exactly such a scenario multiple times and with different combinations of partitions being unmounted, via Tracker and via DriveSetup itself. What happens if you try to mount just that partition? In any case I need more information. If have one NTFS partition which mounted once in DriveSetup (Mount all feature) and then not anymore in subsequent tries, while other partitions (BFS and ReiserFS) mounted fine. Trying to mount the NTFS partition individually gave me a "Permission denied" error (WTF?!). The "Mount all" feature as such works like intended.